This invention relates to vane compressors adapted for use in air conditioning systems or the like, and more particularly to vane compressors of this kind provided with improved camming surfaces which minimize torque fluctuations.
In a vane compressor in general, in which a rotor and vanes carried on the rotor are received in a pump housing having an inner peripheral surface formed as an endless camming surface, the endless camming surface along which the vanes slidingly move together with the rotating rotor, has an elliptical cam profile in the type where the pump housing has two pumping chambers defined therein, and a circular cam profile in the type where the pump housing has a single pumping chamber defined therein.
However, conventionally no particular consideration was given to minimizing fluctuations in the torque acting upon the rotor in designing the cam profile of the endless camming surface. Therefore, the conventional vane compressor has large torque fluctuations during each cycle of suction, compression and discharge of fluid, which causes occurrence of operating noise and vibrations of the compressor during operation of the compressor.
It has previously been recognized by U.S. Pat. No. 4,480,973 assigned to the same assignee of the present application that a cam profile satisfying the below-mentioned requirements can minimize the torque fluctuations:
(1) The compressor stroke length should be as large as possible;
(2) The timing of an increase in the compressing pressure in an initial low torque region of each operating cycle should be advanced so as to obtain increased overlapped portions of the torque curves obtained by the individual vanes. Consequently, the torque fluctuations obtained by the individual vanes are averaged to provide a generally flattened torque curve; and
(3) The amount of protrusion of each vane from the rotor should be small enough to effectively reduce the value of peak torque during the high pressure compression stroke.
In order to satisfy these requirements, the above-mentioned U.S. patent has proposed a camming surface comprised of a plurality of successively arranged curves having respective cam profiles obtained by different equations. However, according to the proposed camming surface, adjacent ones of the curves have their joining portions different in curvature from each other, which can cause jumping of vanes and consequent chattering of same and damage to the tip of vanes or the camming surface.